Ok, so I am going up against a WoC army that is heavy on Chaos Warriors and Marauders in a few days. Which Lore should I use on my Slann to best counter them? I can't decide between Life of Light, but if any other lores are good against them, please let me know.
Metal is very strong against them. The Warriors have a minimum armor save of 4+ (3+ with shields), so that's what you'll need to roll to wound them with Searing Doom. Their armor will be useless. Knights, if he has any, will go up in a puff of smoke. The Golden Hounds can also chip away at his characters if he fails his LOS rolls, but still puts wounds on the unit either way. And remember, any large unit deserves a blast from Final Transmutation. Marauders aren't nearly as vulnerable, but then again your Saurus can get them. When you do get into combat, Plague of Rust and Transmutation of Lead will keep you ahead of the game. Metal isn't as universally useful as Life or Light, but against the good armor saves of WoC, it's a good offensive selection.
Of course there is the morale dilemma of the fact that you are not supposed to choose your lore with your opponent in mind in this edition of warhammer people seem to keep posting lists without magic lore stated etc its a rule that people are struggling to get used to. Yes metal probably is the best choice against WoC but would be useless against others, you should probably look at the lore that benefits your army most (which usually is either Light or Life for lizards) However if both you and your opponent are aware of changing your lore to suit the game I suppose thats ok. Yeah I would choose metal probably.
I had really good luck with shadow against them this weekend. Withering them and then hitting them with sallies was fun. Getting wither and enfeeblling off makes them warriors of wimpdom and your saurus will eat their faces. Okkams will make your saurus strong enough to tear through their armor. Melkoth's can help you out too. Pos and Pendulum won't do anything and steed will be situational, but the debuffs will frustrate your opponent.
I don't agree with Hivor. You are only required to announce your lore before the game, not while making a list. In tournaments it's a given to choose the lore that will benefit you. The Slaan would surely pray for spells that would best hurt his enemy
Check Pages 29, 134, and 162 of the main rulebook. It makes it very clear on each of those pages that you're supposed to pick your lore at the time you write your army list. Granted, some tournaments don't play it that way, but it's as much a part of the rules as anything else.
Tournaments recommend for you to write up fluff over your army as well as have it themed. Not only does it feel better to use, but it’s much fairer to your opponents. When I play I show my opponent my list but not magic items and vice-a-versa. Just stops people in the heat of the moment to have a lying streak (I've had it before and stopped the game by turn 3). And yes it specifically states that you write up your chosen lore in your list. Tournaments don’t mention it anymore as it is in the rulebook. If you could choose your lore per opponent, it wouldn’t be a test of your playing ability. Lloyd